The present invention relates to a method of positioning a planar multi-joint industrial robot.
Conventionally, repetitive accuracy in practical work, specifically, in braking for positioning such a robot, has been regarded as of major importance. This is because, after the initial positioning of the robot has been performed by teaching, normal working movement is carried out as taught.
Recently, however, since a computer-aided design technique has been widely used, it has become necessary to perform point designation on a moving locus using absolute coordinates without effecting the teaching work. Even if point designation using such coordinates is effected, there has been a limit in positioning accuracy due to the accumulation of errors in the arm lengths of the robot and errors of various parts occurring during the assembling of the robot.
A technique for ensuring the positioning accuracy of the robot is disclosed in an article "Method of Measuring Various Dimensions of Robots by Teaching" in the papers of the Autumn 1981 Meeting of the Japan Society of Precision Engineering. The article discloses that the actual dimensions after the robot has been assembled are used so as to cancel errors caused in the process of assembling the robot to thereby improve the positioning accuracy during the actual movement of the robot. Even if the errors at the robot side are corrected, however, it is impossible to ensure sufficient positioning accuracy in actual work because the relative positional relation between the coordinate systems of the workpiece object and the robot cannot be accurately maintained in practical use.
On the other hand, generally the coordinate system of the robot does not coincide with the coordinate system of the object when the robot is located at the working position. A technique making the coordinate systems agree with each other and wherein input is effected in the coordinates of the object has been proposed in Japanese Unexamined Patent Publication No. 60507/1984. According to this technique, the teaching work is simplified so as to shorten the teaching time.
As described above, however, because the accuracy of the robot is not sufficient, high positioning accuracy cannot really be ensured.
An object of the present invention is thus to ensure high positioning accuracy, even for an input employing an absolute coordinate system, by correctly determining errors in the process of assembling the robot and the relative positional relation between the robot and the object for work by the robot in actual use.
According to the present invention, during the assembling of the robot, the arm lengths and the angle at the junction portions of the arm are obtained by measurement and stored as correction values, and in setting up the robot, amounts of offset and inclination between the respective coordinate systems of the robot and the workpiece object at various points are obtained by measurement and stored as further correction values, whereby the data of the operating program for the robot is corrected by these two types of correction values so as to actuate the robot to operate on the basis of the corrected data. When such correction is performed, data for an operating point of the robot can be input in the rectangular coordinate system of the object, and, moreover, high positioning accuracy can be realized without performing teaching work.